how to compute number of pixels in images

Dear sir I have one ground truth image(image 1) and other segmented image(image 2). I want to compute the number of pixel for white area for image 1 and number of pixel for red area in image 2. and then want to compute the difference of pixels.

[Adam]

If the black pixels are all 0s then just use

doc nnz

If they aren't you can still just easily count, for example

nnz( myImage == 7 )

[Gianfrancesco Angelini]

There are many ways to do it. I will suggest you a basic one, hoping to be clearer and helpful

% Define your images
img1 = x1;
img2 = x2;

% Convert them in grayscale, easier approach
img1g = rgb2gray(img1);
img2g = rgb2gray(img2);
figure(); imshow(img1g);    %if you want to see the result
figure(); imshow(img2g);    %if you want to see the result

% Calculate
img1g_totpx = numel( img1g );           %total number of pixel of img1
img1g_NB = length( img1g(img1g~=0) );   %number of pixel not black of img1

img2g_totpx = numel( img2g );           %total number of pixel of img2
img2g_NB = length( img2g(img2g~=0) );   %number of pixel not black of img2

diffPx = abs( img1g_NB - img2g_NB );    %difference of pixels between the 2 imgs

Cheers

Answer 1

[Image Analyst]

Because a different person asked this very same question with the very same image, and Walter answered it here I'm thinking it's homework. I've tagged it as such.

http://www.mathworks.com/matlabcentral/answers/8626-how-do-i-get-help-on-homework-questions-on-matlab-answers

[Walter Roberson]

It was the same person, posting twice.

[Image Analyst]

Oh, you're right. He posted it in someone else's discussion. I just saw the original poster's name.